The role of cyclic nucleotide-generating systems to the functional operation of central nervous system is being investigated from a number of standpoints: 1) Alterations in the levels or properties of brain adenylate cyclases, phosphodiesterases and protein kinases as a result of pretreatments of animals with drugs, hormones, or environmental manipulation. 2) The nature and homeostatic control of cyclic AMP and cyclic GMP-generating systems in brain slices with emphasis on the types of neurotransmitters and antagonists which interact with the systems. 3) Correlation of effects of drugs on the function of cyclic AMP and cyclic GMP-systems in brain slices and cell-freee preparations with in vivo effects of the drugs on behavior and vegetative function. 4) Strain and species differences in the magnitude and character of responses of cyclic AMP-generating systems in brain slice to catecholamines, serotonin, histamine, adenosine, prostaglandin and depolarization and the sensitivity of such animals to drugs affecting these neurotransmitter substances. 5) The nature and control of the interactions of ions such as calcium, magnesium, manganese and zinc with the cyclic nucleotide-generating systems of brain.